An elm function to calculate some appending function over the diagonals of a matrix (represented as a List (List a)))

DiagonalAppend.elm

module Main exposing (..)

import Html exposing (text)
import Math.Vector2 as Vec2 exposing (Vec2, vec2)


type alias Point =
    { location : Vec2, velocity : Vec2 }


distributeForce : List { a | location : Vec2, velocity : Vec2 } -> List { a | location : Vec2, velocity : Vec2 }
distributeForce points =
    List.map .location points
        |> fused distribute Vec2.add
        |> List.map2 (\p added -> { p | velocity = Vec2.add p.velocity added }) points


fused : (a -> List a -> List a) -> (a -> a -> a) -> List a -> List a
fused expand append list =
    case list of
        x :: xs ->
            case expand x xs of
                [] ->
                    []

                z :: zs ->
                    z :: List.map2 append zs (fused expand append xs)

        [] ->
            []


distribute : Vec2 -> List Vec2 -> List Vec2
distribute v vs =
    let
        helper v1 v2 =
            let
                d =
                    Vec2.sub v1 v2

                distance =
                    Vec2.length d

                direction =
                    Vec2.normalize d
            in
                ( (Vec2.scale 0.1 direction)
                , (Vec2.negate <| Vec2.scale 0.1 direction)
                )
    in
        List.unzip (List.map (helper v) vs)
            |> Tuple.mapFirst (List.foldr Vec2.add (vec2 0 0))
            |> uncurry (::)


vectors =
    [ vec2 1 1
    , vec2 -1 1
    , vec2 1 -1
    , vec2 -1 -1
    ]


main =
    vectors
        |> List.map (\v -> { location = v, velocity = vec2 0 0 })
        |> distributeForce
        |> toString
        |> text